Storms & Global Warming II

Earlier this year, we posted two discussions on the association between climate change and storms: Storms and Climate Change and Some recent updates. I will use the abbreviation TC here in the loose meaning of a tropical cyclone. These posts discussed the high number of TCs during the previous hurricane season and an essay on the relation between TCs and climate change. The uncertainty surrounding trends in storminess was underlined, and a point was being made about this subject being controversial.

There are also some further differences. Chan and Liu (2004) argue that current models are not yet sufficiently good for addressing the question regarding global warming and typhoons (A typhoon is technically the same as a hurricane, the difference being that they form over the western Pacific or the Indean Ocean). But the GFDL study is based on a state-of-the-art high-resolution model that is more appropriate for hurricane studies and provides important evidence suggesting that climate change may have an effect on the TCs. Chan and Liu (2004) point to a lack of positive correlation between SSTs in the western part of the tropical pacific and the typhoon activity in the western North Pacific. They argue that the typhoon activity is related to El Ninos and that higher moist static energy provides conditions favourable for TCs. The atmospheric flow will also have an influence, as strong vertical wind shear can inhibit cyclogenesis (spawning of cyclones). I will not draw their analysis into doubt other than that I believed that they incorrectly framed the question. Therefore, I believe that there could be a different interpretation of their results. The SSTs they examined were from the ‘warm pool’ – the region with the highest temperatures in the world (~30degC) and well above the critical threshold of ~27 degC. SSTs in this region are not strongly positively correlated with ENSO. However, the region of high temperatures expands into central and eastern parts of the tropical Pacific during an El Nino resulting in an increased area of SST higher than the critical threshold value, and this aspect is in my opinion crucial to the interpretation. The tropical Typhoon frequency may be sensitive to the area with high SST (above ~27deg C). The clear seasonality in TCs (“hurricane season”) with highest activities during the summer is one of the strongest pieces of empirical evidence that higher temperatures give more favourable conditions for tropical cyclones (After all, TCs only form in the warm tropics…).

One argument is as follows: as the globe warms, the area with high temperatures will increase, increasing the area on which tropical cyclones can spawn. However, climate model studies differ in their account on the tends in TC frequencies. I’m not aware of of any study which correlates the TC activity with the area of high temperatures, but such an analysis would perhaps be more appropriate than just correlating with the SST within one specific region. The notion of more intense TCs with higher temperatures is nevertheless supported by model studies from GFDL.

From NOAA

There have been TCs already in this hurricane season. According to Gerry Bell from NOAA’s, seven TCs during June and July is a new record. NOAA also forecasts a high hurricane activity for the remainder of the season, and time will show if this season will match the 2004 in terms of number of tropical cyclones. But we do not yet know if this constitutes an emerging trend – only hindsight after decades will tell.

Thus, the bottom line so far seems to be that SSTs play a role for the TC statistics (destructive power). The most dominant change in TC activity is related to natural cycles (on inter-annual and inter-decadal time scales), which we would call ‘noise’ in a trend analysis in which the trend would be the ‘signal’. There is little evidence of a trend in the TC frequency, however there are some indications of a trend in the destructive capability of the TCs. Conlusions can differ depending what you look at: frequency, intensity, duration of storms (life times) or destructive potential. Emanuel suggests that the recent upturn in the tropical cyclones’ destructiveness can have two explanations: increased level of intensity (consistent with discussions on Storms and Climate Change and Some recent updates) or longer cyclone life times.

Note that when it comes to mid-latitude storms, there is a different story because they are affected by different types of instabilities (baroclinic) and different conditions.

References

Chan and Liu (2004), Global Warming and Western North Pacific Typhoon Activity from an Observational Perspective, J.Clim.,17, 4590-4602

46 Responses to “Storms & Global Warming II”

“1. Anyone making assertions that changes in climate (whether human caused or not) are responsible for any part of the global trend of increasing disaster losses had better provide some new scientific evidence to back up such claims. Future research may tell a different story, but my reading of the current state of science is that, today, such claims are groundless.”

Is it possible that the evidence is starting to arrive?

[Response:Emanuel’s paper does not use disaster losses, but estimates the power of the tropical cyclones from physical principles and empirical data (physical measurements). It does not rely on insurance statistics, which is another side of the story. This is a very serious issue that should not become a taboo because it is controversial. -rasmus]

You can expect to have increasing destruction in the southeastern USA as there has been a large increase in residences and commercial development in the last few decades. This will happen with or without an increase in storms.

I think the storm to GW issue is important as is the flooding to GW issue. One could imagine an outcome where GW occurrs, but little ill effects occur, or one could imagine a WATERWORLD type disaster. Or something in between. Clearly, the extent to which GW hurts us is what really matters, so figuring out how much of the bad effects result from GW is critical.

All that said, I think dwelling on a particular year (this one) with lots of bad storms is meaningless and smacks of mugging to the camera.

Don’t get me wrong Rasmus I wasn’t criticising either ‘side’. I am aware that two very different datasets are being used.

My point is the selfish one, that for a social scientist looking at societal risk perception and adaptive capacity in flood risk areas, this research represents a dilemma.

I feel that Emanuel should be congratulated for reorientating the research question from frequency to intensity. In doing this he has apparently produced significance where before there was none. This I feel is an abject lesson for all of us…it certainly has been for me.

Conversely, though, the results can still do little to inform the person who is sitting filing their insurance renewal in their home on the sea front. The problem of differentiating the signal of intensity from the noise of frequency remains, and I for one cannot think of a research question that could draw from this data an answer to the “Is AGW causing increases in hurricane losses?” question that this person is scratching their head asking.

RE comments # 1,2,3. Boy, talk about knee jerk reactions. This is a legitimate scientific study, published in a legitimate scientific journal. It is only one piece in a big puzzle. The results still might or might not hold up as more scientists, including global warming sceptics, dissect it.

However, to get emotional and add your own opinions as to this study’s validity as if you researched and published in this topic is hilarious. This is not how science is done…it is how politics is done. Science must be allowed to research in areas that you personally feel threatened about. If not…it is called censorship. Is this what you are calling for?

Rasmus,
I suppose that the area of higher SSTs may be influenced by other items too. I am thinking of e.g. a slow down of the Gulf Stream in the Atlantic. Even if there is equal warming in the tropics, but the heat is not dissipated to the poles fast enough by the ocean currents, the area of high SSTs will increase and more heat will dissipated by other means like TC’s.
There are some variable links between the number (and strength?) of hurricanes and the PDO/NAO/ENSO modes in different periods of the past. As the NAO is also linked to Gulf Stream strength, this may influence the area of high SSTs…

[Response:You bring up some interesting points. I’m not aware of many studies addressing those issues (there are so many journals nowadays, and hard to keep up while producing own papers…) – perhaps they will appear in the upcoming IPCC report? -resmus]

And let’s make it clear, whatever the controversy about some of the effects of GW, it IS happening, and (I think) we are on firm ground with floods, droughts, glacier melt, and sea rise as being caused by AGW. One of the problems with contrarians is they like to take some controversies within fairly robust science and use those to try and throw out the whole of the science – in this case the whole of the science of climate change.

Then the media report there’s a controvery re, say, the frequency or intensity of TC associated with GW, and the viewers think GW has been disproved once and for all.

Hey number 5, I said I support this kind of examination. Sheesh. Why are you going after me? My only slight snark was about the prominent powerpoint slide in the post (which is camera mugging)…would we have a similar prominence if it were an off year?

Burke et al. [1992] has reported the detection of keV electrons and large electric field transients above a hurricane. These various observations all suggest that what is occurring at great depths in the ocean may couple to the ionosphere. The coupling mechanisms was said by them not to be well understood, but it seems probable that “capacitive coupling” through the displacement current my drive conduction currents within the ionosphere [Hale and Baginski, 1987]. How do these couplings appear? Here is a crude static field drawing:

IONOSPHERE

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TROPICAL OCEAN SURFACE
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Ionosphere Ocean Capacitive Coupling above Eye:
............................+..-..+
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What then happens to the microphysics in clouds in tropical storms with such displacement currents?
http://www.ichmt.org/abstracts/Vim-01/abstracts/04-01.pdf
What does CO2 mean as an ELECTRICAL forcing with respect to ion levels on the ocean surface as the carbination comes out of solution and then is redissolved?
Think space weather is not important here with respect to tropical systems? I here have mention that when the solar winds drop below 500 there are increases in activity. Why? Why would the QBO, an ion wind, have an impact on cyclogenesis as William Gray reports? Water has a dielectric constant difference compared to air in capacitive couplings--indeed, colder water has a still higher dielectric constant, relevant with the cold cloud tops of tropical storms.
The big guns study space weather now--all electrical stuff. GOES variant N in equipped with a new Solar X-Ray Imager (SXI) has been developed by the Lockheed Martin Advanced Technology Center to permit the observation and collection of solar data products. It also has The Space Environment Monitoring (SEM) subsystem has been enhanced by the addition of the Extreme Ultraviolet (EUV) sensor, Energetic Proton, Electron, and Alpha particle Detector (EPEAD), the Magnetospheric Electron Detector (MAGED), the Magnetospheric Proton Detector (MAGPD) and dual magnetometers on a 27.9 foot (8.5 meter) long boom. The EPS sensors have been expanded on GOES-N,O,P to provide coverage over an extended energy range and with improved directional accuracy. See:
http://www.ccrc.sr.unh.edu/~stm/AS/Weather_Toolbox/NE_Weather_Primer.html#Sun
http://sec.noaa.gov/ws/
These are ELECTRICAL features. The electron belt is on top of the proton belt, the so called van Allen belts, then there is the upper ionosphere which tends negative and the lower ionosphere that tends positive, and this coupling impact, and space particles attracted to opposing sings and a dance of high energy particles that come with O2 splitting and ozone level increases, namely toward the tropics, while the closing isobars bring particles to the poles . . . all mean that flaring has a HUGE electrical meaning.
If you are not studying CO2 as a CONDUCTIVITY forcing on clouds, Katie bar the door! You just let the horse out of the barn! You miss the hottest stuff in climate. I promise to make some of it real time and real right here on real climate.

[Response:We do not need to invoke these aspects of electric fields and so on to explain cyclones. They can readily be simulated in computer models describing the dynamics and thermodynamics. Cyclones are also routinely simulated in weather models that do not take the electric field into account. The electric field plays a role in terms of lightning and charge separation in clouds, and there are some speculations about condensation to clouds as well. But that is a far strech to the Ionosphere. I have an interesting anecdote: At the turn of the 20th century, a group of scientists managed to convince that processes connected with the northern lights had an impact on the weather, and hence an Aurora observatiory was built on ‘Halddetoppen’ in northern Norway. Nobody has ever managed to establish such a link (at least to my knowledge), however, even after so many years. You are obviously very enthusiastic about the prospect about an effect the ionosphere may have on Earth’s climate, but I’m afraid to disappoint you that I’m not convinced yet. -rasmus]

This is unrelated to the tropical cyclone discussion, but I thought it was related to the discussion of increases in the frequency and intensity of (and areas affected by) severe weather:

TORNADO SPOTTED NEAR SAND POINT (ALASKA) IS APPARENTLY A FIRST
By DAN JOLING, The Associated Press

Residents of Sand Point witnessed a weather phenomenon that elders say is a first-time occurrence.

They looked across Popof Strait to nearby Unga Island last week and watched a tornado touch two uninhabited mountains.

“You could see the clouds twisting and debris spinning off of it,” said Jaclynne Larsen, 30, a teacher at King Cove who returns to her hometown each summer.

Sand Point, population 908, is on Popof Island, one of a dozen or so Shumagin Islands 570 miles southwest of Anchorage near the tip of the Alaska Peninsula and the start of the Aleutian chain.

Larsen was at home with her mother when a friend, Dwain Foster, alerted them to the funnel cloud. He ran up their stairs and told them to grab their cameras.

Sam Albanese, warning coordination meteorologist for the National Weather Service in Anchorage, confirmed that the funnel cloud was a tornado after talking to residents and seeing photographs. Tornados originate in clouds accompanying severe thunderstorms and touch the ground, unlike water spouts and dust devils, which originate from Earth’s surface.

“It’s very rare for the Alaska Peninsula,” Albanese said.

One reason for the small number of reports of tornados in Alaska is the size of the state and the small population, he said.

“If it has happened, it probably wasn’t observed,” he said. “We don’t really have the means to observe this.”

Tornados start in severe thunderstorms, but the National Weather Service’s system for detecting lightning strikes does not extend to the area near Sand Point. It’s the same story for Weather Service radar, which can alert observers to tornados.

Larsen ran outside with her camera, looked to the southwest and saw the tornado.

“It lifted off one mountain and touched down again on another mountain,” she said.

She watched for 15 to 20 minutes.

“It just lifted off of that one and dissipated,” she said.

Larsen, 30, had never seen a tornado on the islands. Neither has her mother or grandparents, she said.

Susan Shoemaker, a police department dispatcher and wife of the city’s public safety director, was in the parking lot of the Alaska Commercial store when she saw the tornado. She had lived in Kentucky and recognized the funnel cloud.

“We all gawked at it for a while,” she said.

Larsen and Shoemaker said the temperature was about 60 degrees and winds were calm. Even more unusual for the island’s maritime climate, it was humid and muggy.

Larsen, who teaches first and second grade, will be incorporating the tornado into her science lessons.

[Response:To put it in a differnt perspective, weather models are capable of predicting clouds and precipitation, without the need of details on electrodynamics. There is no secret that some clouds – like thunder clouds – involve lightning and electrical phenomena. This is most likely a result of the cloud formation rather than electro-dynamical processes causing the clouds themselves (mind you, there are also clouds that produce that rain but do not produce lightning…). The dynamics and thermodynamics are fairly well-understood: convection (updraughts) bring moist air up and the water vapour condenses (usually on cloud condensation nuclei, CCN) as the air gets supersaturated – it cools as it ascends and expands (lower pressure). The electro-dynamical aspects are likely to be ‘bi-products’ of the process – interesting, but there are not much empirical evidence for electro-dynamical processes playing any role in the formation of clouds. Lightning probably play an important role for the ambient (fair weather) electric field that exist between the upper atmosphere and ground. It is believed that a so-called charge-separation must take place for lightening to occur in order to enhance the electrical field in the cloud. The charge separation is not very well understood, but one explanation is that it must involve freezing processes and splintering/fracturing as the outer shell of drops freeze before their core. When the drops’ core freeze, the shell splinters due to expansion of the freezing core. There have been some suggestions that electric fields may enhance the formation of drops (electro-freezing hypotheses; Tinsley and others), but as far as I know, there are no conclusive empirical evidence for this actually occurring in the real atmosphere, and besides, this process may be unimportant as the drop formation could also happen in the absence of an electric field. TCs form in a similar fashion to clouds, albeit in a more extreme fashion due to a instabilities. Again, I do not believe that electro-dynamical processes play an important role in their formation. -rasmus]

“Anyone making assertions that changes in climate (whether human caused or not) are responsible for any part of the global trend of increasing disaster losses had better provide some new scientific evidence to back up such claims….”

I agree with Pielke’s statement. Positive assertions must be backed up by solid evidence. On another thread, I said that the recent heat wave in Colorado seemed unusual in my view and here we are dealing with hurricane intensity and longevity. Rasmus shot me down when I said that about the heat wave — “Even so, they [extreme events] will still happen from time to time, and if there are ‘too many’ record-events, then this is improbable given an iid-process.” Of course, I could not statistically back up what I said. However, this from Pielke talking to the Rocky Mountain News:

Denver is not getting hotter in the summer, and one measure of that is the number of consecutive days above 90 degrees, Pielke said. There were longer stretches of days above 90 degrees back in the early part of the 20th century and the end of the 19th century he said. So we are in a heat wave right now, but we’re not in an unprecedented heat wave. A 12-day stretch of 90-or-above highs ended Sunday, when the mercury in Denver peaked at 86. The city’s longest streak of 90-or-higher days is 18, which has happened twice: in July 1874 and July 1901.

But we also have this statement:

Boulder climatologist Klaus Wolter says the hot spell was the hottest five-day period in Denver history. “It was unprecedented,” said Wolter, who works at the National Oceanic and Atmospheric Administration’s Climate Diagnostics Center.

The clear implication regarding Pielke is that the burden of proof is on the scientists to find statistically significant correlations and otherwise, the negative conclusion is drawn regarding whether climate change is in the mix, be it heat waves or heavy flooding/monsoons or hurricane intensity. If he’s going to say that positive assertions require proof, he can also say that negative assertions are not justified in the face of lack of data and scientific study.

So, the truth is that the data trend has not been tracked and studied in almost all cases. Climate change could be a factor but that is not known — it is becoming more clear in the case of hurricane intensity (if not frequency). So, the honest answer in statements to the press regarding extreme weather events is this: “climate change is happening and is possibly a factor in this weather (or hurricane) event but our current understanding shows no significant (or some) correlation. There may or may not be a connection as our knowledge increases.”

Some blanket statement that climate change is not involved (Denver heat waves, hurricane intensity, record flooding) is irresponsible nonsense since that is not known.

[Response:I appreciate the explanation about capacitance, after all it is a while I completed my first degree in physics and electronics… Actually, I think the issue of electrico-dynamics veers off the subject of the post, although I get Mike Doran’s point that he doesn’t believe so. Yes, I also did my masters in cloud micro-physics some years agao, and if my memory serves me right, electrical phenomena play a role in cloud mircophysics. But not in the way Mike Doran outlines, unless the view has changed completely. I think if it had, we would read about it in Nature and Science. I’m open for new ideas and do not write off the idea of electrical phenomena playing a role in climate – hence a discussion on the subject together with various curiosities such as Aurora, Elves, airglow, Sprites,the Van Allen belts, and Lightening in my book “Solar Activity and Earth’s Climate” (2002; Praxis/Springer). But at this stage, there are still speculations so I think that a simplified view involving capacitance, the sea and the ionosphere can be discussed further on the methanehydrateclub site and not under this post. Thanks for your input Mike! -rasmus]

I think the thing that troubles me is that there are so few studies out there that actually look at real data, and make no mistake about it, model output are not data. Weather is ingredients-based. If you get the right ingredients coming together in the proper measure at the proper time you get the weather. This holds for everything from severe thunderstorms to synoptic and mesoscale-scale weather systems. Global warming is indeed likely to produce significant changes in the weather, but only when the various ingredients change sufficiently to produce a trend. Given the high interannual variability of many severe storm types and the fact that the impacts of GW are very much regional at least for now, trying to identify trends is problematic at best. At worst, it’s a fool’s exercise because in many cases we shouldn’t even expect to find a change in severity or type because the ingredients necessary for such a change to occur haven’t changed suffiently…yet. This is not to say for a minute that we shouldn’t be looking for trends in things like hurricane intensity, just that finding or not finding a trend at this time doesn’t prove a whole lot. It most certainly doesn’t mean that a trend won’t appear 10 or 20 years down the road, just that it may well not be here now. I think that may be some of what Pielke is attempting to say. Sometimes a hurricane is just a hurricane and a tornado is just a tornado and attempting to fit each and every one into some larger contextual framework isn’t possible.

[Response:I would recommend reading the Science article by Kevin Trenberth: Uncertainty in Hurricanes and Global Warming. He discusses aspects of trends in hurricanes. I do disagree in the view that model output is not data. The important question is “what do they represent?” -rasmus]

Re #6: You have this correlation backwards. The Gulf Stream circulation is about equal parts wind driven, which is roughly constant in strength, and deep-convection driven, which varies significnatly on decadal time scales. The majority of the streamlines of this deep convection appear south of the equator, with some of them distributed all over the world, but the largest concentration just south of the Equator, near the coast of Africa.

Consenquently, the associated SST pattern is slightly cooler in the deep convection upwelling regions of the Equitorial Pacific and the Indian Ocean, strongly cooler in the nearest deep convection source region of the South Atlantic near Africa and the Equator, warm over the bulk of the North Atlantic, strongly warmer where the gulf stream loses the largest portion of its heat near 50N 25W, and strongly cooler near 45N 45W, which turns out to be a back-eddy of the Gulf Stream with increased transport of cold water from the north whenever the Gulf Stream is running quickly. The change in the average SST should be slighly negative, as this ciruclation transports extra heat to deep water.

We can check the current SST and see that this matches what is going on currently, except for the cold region near 50N 25W, which was there not too long ago, but has recently disappeared, so we appear to be in a phase of high deep-water convection in the North Atlantic. It would be nice there were more timely reporting of deep convection measurements. Results from ship weather station M appear to indicate an all-time (over 50 years of records) low in deep water production east of Greenland, so presumably the bulk of the convection would have to be in the Labrador sea.

The warmpth in the southern USA and elsewhere north of the hurricane-producing region has been as large a factor in the large number of storms this season as the actual SST where the storms are formed, because it has decreased wind shear.

The decrease in deep-water convection due to global warming fights the overall increase of temperatue due to GW. Overall, I’m enclined to believe that GW is likely to decrease Atlantic hurricane formation rates slightly, while significantly increasing storm formation rates in the Pacific and Indian oceans. This result would be strongly dependent on the exact dynamic response of the Greenland ice sheet to surface meltwater, which is modeled poorly in todays global models.

Re #10: I’m sorry, but this post seems mostly incoherrent to me, and the link to growing crystals in DMSO solutions hardly seems relevant, but you do raise some interesting points. The solar wind, since it is charged, compresses the Earth’s magnetic field and also interacts directly with cosmic rays, and greatly lowers the amount which reach the Earth. When it is low, there will be more cosmic rays stopping in the statosphere, where they form the nuclei of water droplets. This results in more heat-trapping stratospheric clouds, and more hurricanes. This effect has probably become much smaller in modern times, since our stratosphere is now so dirty with jet exhaust.

Correction: Deep North Atlantic slighly INCREASES global SSTs by decreasing the depth of the termocline in the upwelling regions, hence decreasing the ocean’s heat content, resulting an a net increase in emission of energy by the ocean.

Re: #1 – the “pugnatious challenge”, I’ve had no substantive responses to this and I see none here. It seems safe to say that there is no scientific basis for asserting a climate change signal (human caused or otherwise) underlying the decades-long trend of escalting economic impacts related to extreme events. But I remain open to other, scientifically-based perspectives. Yes human influence on the climate is real and we might even now be able to document changes in the behavior of weather phenomena related to disasters (e.g., Emanuel 2005), but we certainly haven’t yet seen it in the impact record (i.e., economic losses) of extreme events. And it may continue to be difficult to identify a climate change signal in the damage record for decades (or longer) into the future. This has significance for how we ought to both debate the climate issue and think about policy. See:

Centuries of hurricane records have been discovered in the rings of southeastern US pine trees. … they searched all the woody tissues for any sudden drops in a particular oxygen isotope: oxygen-18. That is the hurricane signal …

Not only do we have considerable complexity and uncertainty to deal with respect to more intense hurricanes and other extreme weather events, but now I find out that there are multiple Pielkes! My apologies about any mix-up.

However, my original point in #14 still stands. Statements in the mainstream media (TV, print) about the relationship to climate change continue to reflect what I said: since no positive relationship between extreme events has been established, therefore there is no relationship and, given that the climate is changing, the possibility of one is not reported.

I wonder what they’re saying in the Spanish press right now given the extremely hot and dry conditions they are currently enduring? Or what the Indian press is saying about the extraordinary monsoon of the last few weeks?

I am not sure what drives what: ocean currents which invoke air pressure differences or the opposite, or both are working together as the motor of large scale oscillations… What I have read somewhere (I suppose in the ocean currents pages of the Miami University, but their server seems to be down), is that a strong NAO index, with stronger SW winds, pushes warm(er) water far more north, which increases melting, and this slows down the Gulf Stream, leading to a less strong NAO index, and so on…

Something similar happened in the past decade in the Indian Ocean, where the weakening of southeasterly trade winds caused a major circulation of this ocean to wane by nearly 70 percent of its average strength. During the period 1992-2000, the average sea-surface temperature of the Indian Ocean increased by approximately 0.25 Celsius, this may be the cause of an increased monsoon strength here (or more hurricanes on other places)…

This result would be strongly dependent on the exact dynamic response of the Greenland ice sheet to surface meltwater, which is modeled poorly in todays global models.Yes human influence on the climate is real and we might even now be able to document changes in the behavior of weather phenomena related to disasters (e.g., Emanuel 2005), but we certainly haven’t yet seen it in the impact record (i.e., economic losses) of extreme events.

I feel that someone in the Western Pacific should say something about storms there, though this is not the area of my expertise. (Typhoon experts, help!)

I have browsed the papers of Emanuel (2005) and of Chan and Liu (2004).
(Though my institution has subscription of “Nature”, the file of Emanuel’s paper which I got was an incomplete one –no figures, no math formulas, no substantial list of reference. But a complete PDF file is available from the author’s site at MIT (http://wind.mit.edu/~emanuel/home.html ), and a PDF of its supplement is also there.)

Chan and Liu’s paper discusses correlation of year-to-year values between SST and indices of strong TCs. It is a not study of long-term trends. Chan and his colleagues have already discussed the relationship between ENSO and Western North Pacific TCs in Wang and Chan (2002) and other papers. This time they examine whether local SST is important in addition to ENSO, and their answer is “no” in the year-to-year time scale. Their story is clearer when variability in the longer (interdecadal) time scale is excluded. From that part I infer that the correlation between local SST and TC indices is likely to be positive in the longer time scale, though it requires a specific study to establish such a relationship.

I am a little surprised to know Chan’s previous finding that Western Pacific TCs are more active in the El Nino phase of ENSO. My understanding which had not been updated since 1980s was that El Nino suppresses cumulus convection in the Western Pacific and thus suppresses TCs there as well. I still think that the conclusion depends on the target area and seasons. Chan and Liu took 120 – 180 E, May – November. I think that suppression of TCs by El Nino prevails in the western part of the Western Pacific, and mainly in winter and spring.

It is true that the area with SST above 27 deg. C in the Central and Eastern Pacific is larger in the El Nino phase. Probably the high-SST area in the whole Pacific is larger then. But El Nino also tends to suppress TCs in some regions where local SST is high enough. Probably the correlation between the high-SST area and the total TC activity is positive, but it is a result of spatial aggregation of complicated phenomena.

Emanuel (2005) shows the correlation of _smoothed_ time series of SST and “Power Dissipation Index”. I think that the smoothing reduces the ENSO signal, but that it does not eliminate it. Thus it is difficult to connect the discussion of the paper with the “ENSO and the rest” view of Chan and Liu.

Emanuel has made a good effort to compensate for the inhomogeneity of data quality, as he describes in the supplement. But, it is still a difficult issue.
As Morita and Watanabe (2005) reported, the “best track” data shows decrease of the frequency of strong TCs in the 1990s in the area 15-30 N, 120-150 E.
(Morita refers to a data set compiled by Japan Meteorological Agency. I think it is essentially the same as the Western Pacific part of the JTWC data set used by Emanuel and by Chan, but I have not confirmed it.)
In some more detail, TCs with central pressure lower than 920 hPa decreased, those around 950 hPa increased, and those around 980 hPa decreased. Though it cannot be denied that these are real trends, Morita suspects that these are artifacts due to changes in observing practice. Aircraft reconnaissance in the Pacific was phased out in 1987, and since then surface pressure have been determined by satellite image interpretation (Dvorak method) except occasionally by island stations or ships. Morita’s results suggest that the image interpretation underestimates very strong TCs (typhoons) but somewhat overestimates moderate ones (TSs). I am not sure whether this causes significant bias in Emanuel’s PDI. Also, Morita’s observation is about the specific region. Dvorak method may have different sensitivity in different climatic regions.

When we discuss whether the influence of global warming has appeared in TCs, there is a fundamental problem that we are not very sure about theoretically how TCs should react to (greenhouse-gas-induced) global warming.

For middle latitudes, extratropical cyclones are the principal actor in the energy cycle in the atmosphere. Therefore the total power of cyclones (the number times the intensity) in the whole mid-latitude zone should somehow correspond to the global forcing. If the characteristics of transient warming is similar to those of equilibrium warming, the north-south gradient of temperature will decease, and therefore the total power of extratropical cyclones will decrease.
(Things may not be so simple, however, even in this zone. Increased water vapor will provide energy by latent heat release and somewhat compensate for the loss. And perhaps more important role of moistening is to increase inhomogeneity within individual cyclones. Surely the maximum rainfall rate will increase. Also the maximum wind speed may increase despite of decreased average value.)

There is no guarantee for such large-scale determinism for TCs. The essential feature of the tropical atmosphere is cumulus convection, whose individual horizontal scale and time scale are of the order of 1 km and of hours. The largest-scale feature is the Hadley circulation whose upward branch is none other than the collective activity of cumulus convection. The Hadley circulation requires cumulus convection, but it does not require TCs. Whether cumuli organize into TCs, easterly waves, Madden-Julian oscillations or something else, or maybe remain rather random, is not constrained by global-scale forcing.

If we assume large-scale determinism, we can have some conclusions which will be valid as long as the assumption is valid. Emanuel’s previous theoretical work (Emanuel, 1987) assumes that there is a circular vortex coupled with convection, and discusses how strong it would be. The GFDL model has more degree of freedom, but their experiments assume a circular vortex as the initial condition. It is reasonable that results of these studies are mutually consistent.

Global warming experiments with a “20 km grid” (actually spectral) GCM of the Meteorological Research Institute (MRI, of Japan) shows intensification of strong TCs (consistent with the GFDL model study), and increase of the life time of individual TCs (as Emanuel suggests), but also decrease of the total number of tropical storms.
(Unfortunately the only on-line information about that study I have found is a short abstract for the previous AMS meeting (Oouchi et al., 2005). Off-line and in Japanese, there is a little more information in the abstract volume of MSJ 2005 Spring Meeting (presentation Nos. A203 and A204)).
I am not sure whether the collective total power of TCs, or Emanuel’s PDI, increases or decreases as climate warms in that model.

A caveat is that all GCMs as well many TC models (including GFDL’s) that have been used for climate change experiments employ hydrostatic approximation and “cumulus parameterization”. They assume some ways of self-organization of cumulus convection which may or may not be true. Non-hydrostatic, cloud-resolving models are promising in reduction of this kind of uncertainty. But, climate simulation with these models requires much more computer resources than currently available. Whether the society can afford the cost is another problem.

Another difficulty for the 21st-century projection of TCs (and also for the projection of tropical climate in general) is that it is not certain how ENSO behaves as the mean climate warms. With the same scenario of greenhouse gas concentration, some coupled GCMs produce more EN-like climate, and others less EN-like. ENSO may be a kind of “free” mode which can shift either way.

We can say some small thing relatively confidently for those mid-latitude areas which are sometimes affected by TCs. Warmer _local_ SST helps maintain TCs which happen to arrive there. Thus, we will encounter more cases of strong TCs there _unless_ the situation at the area of TC generation changes much.

Here is an example of a changing entropy pattern, just like the increase in hurricane intensity, brought about by microphysics changes which have occurred due directly to increases of CO2 changing the CONDUCTIVITY of oceans. Of course, there are other inputs, and human activity altering bio modulations of those inputs, but my OPINIONS, which I post on our group, our not the opinions of RealClimate. They are my own.

I feel that I should add some clarification to my previous comment (No. 25). What I referred to by the wording “large-scale determinism” a few different relationships. They have similar logical structure, but each of which may be valid or invalid independently of others.

1. Whether the activity of cumulus convection is determined by the variables averaged over the grid box of numerical models (100 km scale for typical GCMs, 20 km scale in the case of “high resolution” GCM of MRI).

2. Whether the activity of cumulus convection in a TC is determined by the dynamics of the TC-scale vortex (as in the Theory of Emanuel 1987, for example).

3. Whether the activity of TCs (TC-scale dynamics and cumulus convection together) is determined by the global climatic condition (SST, atmospheric composition and general circulation).

In any of these, it does not mean that every small-scale detail is determined by the large-scale condition. (Thus it is not rigorously “determinism”.) It means that the collective effect of small-scale phenomena relevant for the large-scale is determined by the large-scale condition. Also, it does not mean that the cause-and-effect relationship is one-way. It is probably mutual. But, if the result of mutual interaction, in a coarse-grained view, can be interpreted in the function of large-scale variables only, it can be said to be “determined by the large-scale” in a sense.

Large-scale determinism is one of good ways of framing hypotheses. If it is correct, it makes theoretical discussion simple and numerical modelling economical. On the other hand, it is not guaranteed to be valid. I think that it is good that some scientists endorse it and some others are critical to it. Both activities are necessary to promote our understanding of climate.

(Excuse me for deviating from the subject of the original posting.
I think that what I would like to say does not fit in other active threads on solar forcing, and that it is relatively more appropriate to remain in Rasmus’s thread.)

Re #26: I do not fully understand the reasoning of Mike Doran involving electric fields, and I tentatively agree with Rasmus’s remarks (on #10 and #12) about that.

Even though I think that the “cloud chamber” mechanism are at work in nature (as suggested by Svensmark and others), I expect that its magnitude is not significant among many kinds of forcing to the climate system. Rasmus’s article here on 6 Dec. 2004 (No. 42) demonstrates that it is not the dominant forcing driving the global mean air temperature. Its effects on precipitation and atmospheric disturbances are still arguable. I guess that it is much weaker than the aerosol effect (mentioned below), but I do not have a demonstration yet.

I think that cloud microphysics does matter to climate. While I do not think that GCMs (as available today) are useless, I think that their results will be revised somewhat when we know more about clouds. I think the largest problem is the effects of aerosols which act as cloud condensation nuclei. In the context of IPCC, it is known as “indirect effect of aerosols.” The IPCC WG1 2001 report posed the problem, and now experts are tackling it. In that context mainly their effect to the global mean temperature is argued, but their effect will surely modulate disturbances –TCs included– as well.

I think that this is also likely to be one of the major pathways connecting solar variability to climate. Variation in the ultraviolet part of solar radiation modulates photochemistry in the stratosphere, and some products of the reactions can modulate cloud microphysics. I do not know direct evidence about cloud condensation nuclei, but some suggesting modulation of chemistry of the lower atmosphere. As cited by Bradley (1985, Section 5.5.4; but not in the 2nd edition of the book), Zeller and Parker (1981) found 11-year cycles in the time series of nitrate content in the ice at South Pole. Watanabe et al. (1999) found the same signal at another location in Antarctica. Watanabe et al. (1998) found similar variation of hydrogen peroxide content. Probably this effect is usually masked by variations in anthropogenic, volcanic or biogenic aerosols, and is revealed only in Antarctica where other signals are quiet.

(Solar-cycle variation of nitrates also suggests that we do not require global-scale variation of temperature to explain some geological evidence of past solar cycles in lake sediments or shallow sea sediments. It may suffice that nitrogen was the critical nutrient for the aquatic ecosystem in that area.)

He contends that, “Consider the recent Nature article. If hurricanes had doubled in power in the last few decades as Emanuel claims, the change would be obvious; you wouldn’t need a weatherman to know which way this wind was blowing. All of these feuding scientists would have agreed on the facts long ago.

“Damages caused by doubling the strength of hurricanes would be massive and increasing dramatically. Figures on this are pretty easy to come by, at least in the United States. The insured value of property from Brownsville, Texas to Eastport, Maine — our hurricane prone Atlantic Coast — is greater than a year of our Gross Domestic Product. If hurricanes had actually doubled in power, the losses in the insurance industry would be catastrophic.”

He then states, “You would think that reviewers of Emanuelâ??s paper at Nature would have thought to ask whether, in fact, there was evidence for increasingly powerful storms.

“But they didn’t. There is just no incentive in the scientific community to kill the remarkably fertile global warming goose, a beast that feeds on public fears.”

Does anyone here feel that there is any validity to Michael’s arguement?

[Response:As far as I know, the insurance costs have risen dramatically, but I have only heard this second hand. Please correct me if I’m wrong. It is also interesting to note the new tack taken by the contrarians: the reference to insurance figures has previously by them been dismissed as not a good indicator (according to my recollection). I’m not convinced by Michael’s arguement, but there is a point: if people do not feel the impact of a climate change (say in the future), then it’s not important – yet. Time will eventually tell who is wrong and who is right. The objective of making scenarios for the future (work assessed by the IPCC), is to use the best of our knowledge and foresight in order to avoid making big mistakes that will have a future impact. This is an important endevour for any highly advanced and civilized society. -rasmus]

BTW, Michaels is an EXTREME RWN and is agenda driven, not science driven, IMHO. He has NO education in electrical or biological sciences. Nada.

[Response:Mike, please confine your comments to this site. I will henceforth remove all your links to your own blog under my posts. RC should not be used to ‘advertise’ your own blog (I don’t know if that’s the intension, but I think that is the effect, intended or not). I want to explain my position on this subject: It’s great to use links to refer to published work, news articles, or other peoples essays, but I think it’s not when you point to your own blog where you in effect post a response to RC. Furthermore, by allowing such links would also mean relinquishing some control, and we would face greater risk of objectionable links to unscientific material (as one above that was deleted because of unacceptable personal characterisation). -rasmus]

Michaels op-eds on the Cato site are political lobbying. Cato is a political advocacy group for free-market/pro-industry policies and not an independent academic or scientific institute. Cato and the people and groups it represents are worried if climate change science is widely accepted regulations will be based on it. To prevent these regulations Cato is criticizing climate science. Raising valid questions about the science that regulations are based on is acceptable, but misrepresenting science to affect the political process is not.

Cato and Michaels have a history of regularly misrepresenting climate change science, science generally and environmental regulations. This op-ed by Michaels is no different. He is trying to conflate Emanuel’s measurement of TC intensity with economic damages, but they are different measurements. As a scientist he is not unsophisticated and he does know that these are not the same, but he is saying that these are the same to sway the public and score political points.
His comment that climate scientists are exaggerating anthropogenic climate change to get more funding is worse. He is trying to cover for groups who are fighting climate change regulation mostly because industries (and the lobbying groups they fund like Cato) will lose financially. It’s like fighting kids saying, “I know you are but what am I”.

I personally think there is little validity to Michaels argument. At least it’s not as bad as Spencer pushing intelligent design (creationism) on TCS. I tend to be very suspicious of anything Cato, Marshall, CEI and these other conservative lobbying groups say about science and environmental regulation.

[Response:Thanks for the links, Roger! I guess the question in this case (referring to comment #33 regarding whether there really has been a trend and the reference to Michaels and hurricane loss) boils down to weighing the normalisation of hurricane loss (used to adjust the trends in total hurricane loss) against the calculations by Emanuel as well as the degree of representativeness in this case. -rasmus]

# 36. As you all know by now, I think that tropical storms are part of a living earth which modulates climate electrically. Dampens it.

The most costly storms appear to be Andrew and a storm in 1928.

What I think is extremely important to consider is both Andrew and that 1928 storm followed significant volcanic activity. That would have meant that the atmosphere contained a greater degree of SOx emissions, and then that in turn has significant microphysics meaning.

That is, rainwater has a pH of about 5.6. The cloud material of a tropical storm, of course, contains a great deal of salts from spray against the ocean, and that helps the extreme DC fields between ocean and atmosphere that change microphysics to work in a different dynamic. Consider, again, that the lower ionosphere is relatively positively charged and the coupled regions on the ocean, with opposing charges attracting, become relatively negative. SOx, as in sulpher acids, are essentially a positively charged ion that will exist in the super cooling water droplets in convecting clouds. Those clouds will find more intense microphysics changes near the negative aspect of the capacitive coupling–namely on the ocean surface, given that the ionosphere is positively charged by thunderstorms globally. It is no accident that the surface mesovortices winds of Andrew and the 1928 storm were so intense. Meanwhile, a storm like Bret which had a landfalling BP similar to Andrew, essentially had low near surface winds, and was a substantial flooding storm, capable of moving inland without slowing as much from the friction of interacting with land. The danger of storms, therefore, that come outside of periods when there is high volcanic activity is flooding and stalling. The danger from storms that occur relative to volcanic events, on the other hand, with high SOx emissons is wind damage. This is how Andrew was what it was and Mitch was what it was.

Again, if you do not look at the MECHANISM of cloud organization, you fail to see the significance of the volcanoes, or the significance of higher CO2 from human activity and what that added CO2 means for more intense storms.

It also should be pointed out that in terms of assessing the damage from a ‘storm’ what that storm means in relation to a living earth–all of the earth. If there is a terrible drought and no hurricanes, such as in the 1930s, you can make a conclusion about climate change not warrented, as the 1930s gets to biological changes brought about by human activity and hydrology, namely dams and levies and man made lakes with the Mississippi, Rio, and Colorado rivers. Human activity and CO2 has a general meaning, having to do with conductivity meanings in the oceans, particularly a signal in lower salinity zones in the oceans, where the relative ion count increases. That is why the Pacific high has been so impacted, for instance.

[Response:Were there any volcanos last year? There were quite a number of TCs then. It’s important to look at a large number of cases, rather than just a couple, before you can test any hypotheses. You need to demonstrate that there is a significant increase in TC activity after volcanic eruptions (I must admit I doubt it). I suggest you get down to the statistical analysis and that you explain (model) exactly how the microphysics is affected by negative charges (you say its more intense – that’s not very informative!) and how the microphysics affect the dynamics and thermodynamics on larger scales. You then need to make direct measurements (eg penetrating clouds) to document whether your model actually has predictive skills. As far as I know, there are not many others who has a similar view on this subject, but you can only convince the society through predictions and verifications through empirical evidence. Before that, your ideas are pure speculations. Until then, I think that we have covered most of the aspects on electro-dynamics and storms. So, good luck with your modelling and field work! I’m looking forward to your publications in peer reviewed literature! -rasmus]

Re #34: [BTW, Michaels is an EXTREME RWN and is agenda driven, not science driven, IMHO. He has NO education in electrical or biological sciences. Nada.]
If the comments (above)cannot be backed maybe they should be deleted entirely. The following comes from one of the web sites about Patrick J. Michaels. I trust that the EDUCATION part is accurate.
{He holds A.B. and S.M. degrees in biological sciences and plant ecology from the University of Chicago, and he received a Ph.D. in ecological climatology from the University of Wisconsin at Madison in 1979.}

Another question we must ask is: will greater numbers of hurricanes of Category 4 or 5 strength make landfall as a result of climate change (due to SSTs warming along with, but at a slower rate and with some time lag as, the atmosphere)? Also, will the hurricane season be increased as a result of climate change (which will raise SSTs above the c. 26 C mark necessary for the development of TDs, TSs, and TCs)?

Whilst I agree broadly with your conclusions, we have to be a bit careful because the frequency of hurricanes varies on decadal timescales and any impact of GW will be superimposed on such background variability.

Therefore it is entirely possible, in fact I would say to be expected, that we will see hurricane numbers and intensity decrease again within a few decades. We might expect the minima reached in the next cycle to be higher than the minima in the last cycle, but it is important to stress this complexity otherwise people will accuse scientists of crying wolf when the 2030s are ‘unusually’ quiet in terms of hurricane frequency.

There is also the possibility of more complicated circulation interactions which might inhibit tropical cyclone formation [eg wind shear which, in the Atlantic, is affected by ENSO].

Also, I’ve heard it stated that frequencies of tropical cyclones have *declined* in other regions, though whether any decadal/other timescale natural variability is ‘known’ of, I don’t know. Certainly it reinforces that a simplistic warmer oceans -> more and stronger tropical cyclones is not the whole story.

Re: #40

We might also ask how much worse a comparable event would be were sea levels already 0.5m higher to begin with… Or whether a much weaker tropical cyclone [and therefore one likely to occur more often] could cause comparable damage with the sea level already much higher.

It is also worth remembering that the earlier we start cutting emissions the cheaper it will be to do so and we will also be able to reach a lower stabilisation level for CO2 in the atmosphere.

Re #43: On your Re #40, that is indeed the chief point. The sea level rise alone will probably be entirely manageable, excepting areas such as the Maldives, Chuuk etc. Couple it with coral dieoffs due to elevated (or dropping?) water temperatures and with an increasing frequency/severity of TCs, and you’re headed for trouble.

Re #31: It is quite certain that weather is a largely non-linear (AKA chaotic) process and/or that weather patterns are emergent, that is, they cannot be reconstructed from their constituents because the data needed is not exact enough in quantity and quality. Note that non-linear processes are theoretically calculable, but extremely dependent on initial conditions.

The question is, does that hold true for climate as a whole, too?

FWIW, my best guess is that the difference between weather (which cannot be predicted reliably for more than a few days no matter how much computing power you throw at it, and due to the data quantity/quality problem, it may well be technically impossible entirely under real-world conditions) and climate (which can be much better predicted on a global scale for a longer period of time with a higher degree of accuracy – still, a few years are the technical limit) is a difference of scale. Figuratively, the size of the phenomenon in question in relation to its surroundings. Individual weather *patterns* are about as non-deterministic as anything gets; the European heatwave in 2003 was neither foreseeable as to when it would start, nor as to its duration – when things finally turned normal again, we knew only a few days in advance that they would do so.
If I am correct and it is chiefly the phenomenon/influences difference that makes climate much more calculable than weather on their respective scales (mega to macro vs meso), I’d further wage the guess that with increasing perturbation, the deterministic ‘component’ of climate will decrease and the chaotic behavior will increase. It is clear that climate is a complex system and in all likeliness it has some deterministic and some non-deterministic components. When observing such systems in general (social, economical, ecological… systems), the usual behavior when perturbed is to react less than might be expected due to internal dampening until a compensatory capacity is breached, then flip into a pronounced chaotic state and sooner or later attach to a different attractor, that means, stabilize again. Most violent revolutions and drastic ecosystem changes are preceded by a period where ‘the lid is kept down’, i.e., there is less thange than would be expected in a deterministic system due to inherent stabilizing mechanisms. When the ‘point of no return’ is breached, collapse occurs in a relatively short period of time (for climate, that would be many decades to a few centuries). From what data exists about previous peroids of rapid climate change (i.e. climate change caused by an intrinsic mechanism such as a meteor impact, massive volcanic activity or human activity, as opposed to sun cycles), it seems that climate does show such behavior too. Preceding and following the point of collapse are periods with a high incidence of fluctuations, usually omnidirectional (the summer of 2002 in Europe was one of the coldest and wettest on record, the following one the hottest and driest ever recorded), but not unusual or novel per se on a system-wide level.

The worrying point is that including a rough estimate of permafrost-methane based forcing, what we’ll get until 2100 is pretty close already to being the largest fluctuation in climate patterns ever since the start of human civilization, i.e. it will probably be outside everything we take for granted and the basic ‘natural laws’ (which they are not, obviously) that every civilization on earth was based on. In such a case, it would remain to be seen whether the intrinsic dampening mechanisms of civilizations are sufficient or whether interdependence of social and economic factors actually makes societies more vulnerable. Suffice to say that I consider it improbable to the extreme to assume high-flying dreams things like space colonization will seriously get underway in the next centuries (if not in this millennium or at all, because if push really comes to shove, we’d have to start everything anew from the late middle ages, only this time without oil).

Altogether, I find it really heartbreaking that ‘we’ (humankind at large) currently seem to place all out bets on the simple assumption that if it hits, it won’t hit too hard – after all we came through and with not sufficient oil left to build up another plastics-based global civilization, this one shot we’re currently in really seems to be the only one we have. It would be better if we started to tread lightly soon, like maybe yesterday.

RE #40 to 44:
I was not talking about global warming. My only question was how much damage is due to being below sea level? The point raised about the sea level being 0.5 metre higher has no bearing – New Orleans will be totally evacuated with the current sea level. With respect to the headline “Hurricanes Growing More Fierce Over Past 30 Years”, that is misleading as 30 years ago there was SST cooling and the hurricane activity had decreased. We are now in a SST warming phase, which is independent of global warming, and which was predicted. This year is not the end of the increased activity, so the southeastern USA should be prepared for large disasters. In #44, I disagree with the statement that climatological forecasts over a few years are more accurate than daily forecaste over a few days. Show me the figures.